On all Duets, the motor current will be reduced to idle when there has been no movement of any motor for the idle timeout (default 30 seconds). If this is unacceptable, you can increase the idle current percentage using M906, either permanently in config.g (e.g. to 60% instead of the default 30%) or temporarily in pause.g and then restore it in resume.g and cancel.g.

On the Duet Maestro, in addition the stepper driver chip reduces the current to the standstill value when the driver has had no step commands for a significant fraction of a second. the default standstill current is 75% of the normal current.